Topic: Smaller sprocket in front for higher revs !

[Viktor.J]

Hi !

I have a thought. Would it be any problem to change to a smaller sprocket in front ?

let me explain why.
I never uses the bikes "full speed" , When riding the highway Im about 4-5000 rpm in fifth gear. These bikes generally goes best above like 3000 rpm and now a days im driving in the city resulting in often rpms below 3000. Therefor I thought of changing to a smaller sprocket in front to rev a little higher at low speed and sacrificing the top speed.

Any problem with this ?
accept the gear chart on the forum is there any where I can quickly calculate the speed at given rpms with different sprocket sizes (without opening my old school books)

[mAd mOrdigan]

We always do this with our newer sportbikes... -1 gear in front and some will also do +2 teeth in the back. Accelerates much better and like you said will sacrifice top speed. But why not just shift later and stay in the lower gears longer.. or am i missing something?

[jpfrk2001]

We always do this with our newer sportbikes... -1 gear in front and some will also do +2 teeth in the back. Accelerates much better and like you said will sacrifice top speed. But why not just shift later and stay in the lower gears longer.. or am i missing something?

In a taller gear, you can use a broader range of speed with out needing to down shift due to being a little lower geared. Does this make sense?

[Viktor.J]

my "rev window" at low speeds are wuite narrow. 30 km/h in first gear the bike is lugging, 50 km/h in second gear the bike is lugging and first gear around 5500 which is to high for city crusing. By decreasing the sprocket size in front I would widen the window and when driving 30 Km/h in first gear the rev would be at around 3500 and 50km/h in second gear would be around 4000 rpm.

[bryanj]

Honda originally had a 16 tooth front sprocket but decided it was one of the reasons for chain breakage and went to 17 tooth, might want to think about that

[Viktor.J]

18 is stock on a cb750 K2. ( that's what I drive)

It's a god thought, but with a well maintained modern quality chain that wouldn't be a problem, or would it ?

[ekpent]

Lots of guys go to the 17 tooth on the 750. Not that hard to give it a try and easy to switch back and forth given your riding situation. Should raise the RPM by around 500 compared to the 18 I believe.

[mAd mOrdigan]

We always do this with our newer sportbikes... -1 gear in front and some will also do +2 teeth in the back. Accelerates much better and like you said will sacrifice top speed. But why not just shift later and stay in the lower gears longer.. or am i missing something?

In a taller gear, you can use a broader range of speed with out needing to down shift due to being a little lower geared. Does this make sense?

perfect sense

[SohRon]

A larger sprocket in back vs smaller front sprocket will net the same results and place less strain on the chain. At least that's what I was told when I asked the same question. Something to consider.

[bjbuchanan]

Perfectly fine to switch up the sprockets, tune them for where you ride. Unless you tour a lot the 17 is sounding like the way to go

[lucky]

Yes to lower the gear ratios changing the countershaft sprocket to 1 less tooth IS the easiest way.

[scottly]

18 is stock on a cb750 K2. ( that's what I drive)

It's a god thought, but with a well maintained modern quality chain that wouldn't be a problem, or would it ?

17/48 is a good compromise for me. 16/48 is fine around town, but is a bit too low for extended high-speed cruising at speeds of 65-75 MPH in my experience. The smaller the front sprocket, the harder it is on the chain. Chains have a maximum critical speed based on the diameter of the sprocket; my friend and I found out about this fact after his V-8 sidewinder 3 wheeler spit out it's primary chain onto the highway after a quick blast. I just had my book that lists the critical speeds of various chains returned to me, so I will have to look up 530 chain.

[andy750]

I have a 1972 CB750K2 and a 1974 CB750K4 and they both have 17/48 stock set up. Really is the best way to go as Scottly points out. I can ride on the highway all day with this set up (yesterday was on the K4 for a 364 mile ride to the mountains) with rpms in the 5000-6000 range at 70-85 mph.

In June it was a 3000 mile round trip ride down to North Carolina on the K4 again with no issues on the highway - can pass just fine . No buzziness/vibrations - helps if you tighten up all those loose bolts once in a while.

When I had the K4 in Europe I was on the German autobahn (no speed limit for most of it) for hours at a time ~100mph for a lot of it with high rpms - again no issues.

Change to 17t on the front you wont be sorry.

Andy